The present invention relates to bifocal contact lenses and particularly those of a fused construction, that is, lenses of the type in which the bifocal segment is formed as an insert in the lens by being cast in place and joined to the remainder of the lens without the aid of the adhesives. Other types of bifocal contact lens are known, particularly those in which, for example, the front surface has a secondary or compound curve, that is, a different curvature at one part of the front surface than at another part. Lenses of this type do not form a part of the present invention, it being well recognized in the art that fused bifocal lenses are different in many ways from other, non-fused types of lenses.
With the advent of small diameter corneal contact lenses, greatly increased use of contact lenses has occurred. It is estimated that at least 5 million and perhaps more pairs of contact lenses are now in use in the United States alone. Up until the present time, the majority of contact lenses have been single vision types, although bifocal contact lenses in various forms are known in themselves. One problem has existed, however, which has been a drawback to heretofore known types of bifocal contact lenses, and this problem is referred to in the art as "jump." The expression "jump" refers to the phenomenon which takes place when the line of sight crosses the segment line, that is, the boundary between the far vision and the near vision segments of the lens, and in particular, the part of the boundary defining the inner edge of the bifocal segment. As a result of such "jump," the wearer of bifocal contact lenses has had a somewhat annoying or unpleasant sensation when shifting his line of sight from one segment to the other.
As a result of this known drawback, there have been a number of efforts to solve this problem. So far, the efforts expended in this field have been known to succeed in providing a lens in which jump was eliminated at only one point on the segment line, commonly the point thereof lying at or just beneath the center of vision line of the eye, assuming the lens to be centered with respect to the eye and in its desired position of use. However, in these constructions, the phenomenon of jump still occurs whenever the line of sight crosses the segment line at any point other than the single point in question. Accordingly, in any task in which eye movement is predominantly from left to right, such as a typing job wherein a typist views material to be typed in a series of right-to-left eye movements, the phenomenon of jump is very annoying and tiring to the eyes. In addition, in a concentric bifocal lens, so-called because the bifocal segment is a continuous ring or toroid extending around the far or distant vision segment, a scattering or halo effect resulting from segment line jump is commonly observed upon viewing lights at night, such as when driving an automobile. No systems have been known to have been produced, or even proposed on a theoretical basis, in which the jump could be eliminated entirely around the segment line. Accordingly, there is a significant need for such a lens.
Another disadvantage of other known types of bifocal contact lenses is that the material comprising the far vision segment has in some cases been formed from a higher index of refraction material, which is notoriously unstable dimensionally. Lenses of this type have also been difficult to produce and are therefore undesirable from a manufacturing standpoint.
For the foregoing reasons, and for other reasons, and because of the shortcomings of certain prior art construction in fulfilling the desired characteristics of a said bifocal contact lens, it is an object of the present invention to provide an improved bifocal contact lens characterized by a lack of jump throughout the entire extent of the segment line or surface defining the inner portion of the bifocal segment of the contact lens.
Another object is to provide an improved method for forming such lenses.
A still further object is the provision of a contact lens of the fully no jump type in which the bifocal segment totally surrounds the central, distant vision segment.
Another object is the provision of a bifocal contact lens having a bifocal segment extending only partially around the far vision segment, and in which there is no jump across the entire extent of the inner portion of the segment line or surface.
Another object is the provision of an improved bifocal contact lens which is of particular advantage to users whose occupations call for frequent lateral eye movement into and out of the near vision or bifocal segment of the lens.
A further object is the provision of a lens which is dimensionally stable by reason of its construction.
A still further object is the provision of a method for making such lenses in which full advantage may be taken of existing materials to provide lenses of characteristics not heretofore able to have been achieved as a practical matter.
Another object is the provision of a bifocal contact lens in which the center of curvature of the front face of the bifocal segment lies on a line extending from the center of curvature of the lens rear or base curve to the segment surface or line separating the distant vision portion centrally located in the lens from the near vision segment of the lens which is disposed radially outwardly of the distant vision segment.
A still further object is the provision of a method of forming a contact lens wherein a cylindrical blank is rotated about a given center line and a front curve imparted thereto by moving a tool in an arc about a point radially offset from said center line, in which an opening is then cut in the center of the resulting blank of a size desired to provide a distant vision segment, in which a mass of fluid material for forming the remainder of the lens is cast in place covering at least a portion of said blank, including the front surface portion and the opening therein to form a composite blank, and in which the resulting composite blank is cut to form a contact lens such that rear base curve thereof comprises portions of both near and far vision segments in which the front surface comprises entirely material from which the far vision portion is made.
A further object is the provision of a method for forming a no jump bifocal contact lens blank which includes forming a near vision blank according to a predetermined pattern, and covering a portion of the near vision blank with material comprising a distant vision forming element, so that a lens having predetermined characteristics not heretofore attainable may be cut from the resulting composite blank.
A still further object is the provision of a no jump bifocal contact lens having single radius front and rear curves.
Another object is the provision of a fused bifocal contact lens having the major or far vision portion thereof made from a lower index of refraction material than the material comprising the bifocal segment.
A still further object is the provision of a bifocal contact lens which may, by reason of the manner in which curves defining the bifocal segment are formed, include a bifocal segment portion of greatly reduced thickness, thereby resulting in a lens having a greater proportion of low refractive index material and greater dimensional stability.
A still further object is the provision of a no jump bifocal contact lens having a bi-curve or similar surface defining a portion of the bifocal segment of the lens.
Another object is the provision of a method which is equally suitable for making no jump concentric bifocal lenses and no jump bifocal lenses having bifocal segments in the form of only a portion of a ring, and defined in part by surfaces having at least two characteristics, different forms.
A still further object is the provision of an improved method of making no jump bifocal contact lenses as well as composite blanks from which such lenses may be made.
The present invention accomplishes these objects, and others inherent therein, by providing a bifocal contact lens in which the center of curvature of the front surface of the bifocal segment lies on a line extending from the center of curvature of the base curve of the lens to that portion of the segment surface separating the distant vision segment of the lens from the inner edge of the near vision segment, and by providing a method wherein a near vision segment blank is formed with a front curve and a central opening therein, in which a distant vision portion is formed thereover to create a composite blank, from which a finished lens may be made by forming a front lens curve and a rear lens curve such that the center of curvature of the bifocal segment front surface will be on a line extending from the center of curvature of the rear lens surface to the inner surface of the bifocal segment.
The manner in which these objects, and other objects and advantages inherent in the invention are accomplished will become more clearly apparent when reference is made to the following detailed description of the preferred embodiments of the invention, and to the accompanying drawings in which like reference numerals represent corresponding parts throughout.